Apparatus, system, and method for bad block remapping

ABSTRACT

An apparatus, system, and method are disclosed for bad block remapping. A bad block identifier module identifies one or more data blocks on a solid-state storage element as bad blocks. A log update module writes at least a location of each bad block identified by the bad block identifier module into each of two or more redundant bad block logs. A bad block mapping module accesses at least one bad block log during a start-up operation to create in memory a bad block map. The bad block map includes a mapping between the bad block locations in the bad block log and a corresponding location of a replacement block for each bad block location. Data is stored in each replacement block instead of the corresponding bad block. The bad block mapping module creates the bad block map using one of a replacement block location and a bad block mapping algorithm.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/297,076, entitled “Apparatus, System, and Method for Bad BlockRemapping,” filed Nov. 15, 2011, and issued as U.S. Pat. No. 8,239,714on Aug. 7, 2012, which is a continuation of U.S. patent application Ser.No. 12/419,223, entitled “Apparatus, System, and Method for Bad BlockRemapping,” filed Apr. 6, 2009, and issued as U.S. Pat. No. 8,156,392 onApr. 10, 2012, which claims the benefit of U.S. Provisional PatentApplication No. 61/042,738, entitled “Apparatus, System, and Method forBad Block Remapping,” filed Apr. 5, 2008, each of which is incorporatedherein by reference.

BACKGROUND

1. Field of the Invention

This invention relates to solid-state storage and more particularlyrelates to bad block remapping in solid-state storage.

2. Description of the Related Art

Solid-state storage, as well as other forms of data storage media, issubject to failures of specific regions within the solid-state storage.This type of failure may result in loss of ability to store data in thespecific failed region, but rest of the solid-state storage may functionnormally. Allowing the failed region to be used for data storage wouldintroduce data errors.

Memory cells in solid-state storage are typically arranged in some typeof a matrix of rows and columns. Regions may further be divided intopages, erase blocks (or other block), etc. The pages, erase blocks, etc.may be numbered in some fashion, such as sequentially numbered. Thenumbering may be used in an address to locate a specific page and thenrow and column numbers may be used to access bits, bytes, etc.

When solid-state storage elements, such as dies or chips, are arrangedin an array, the solid-state storage elements may also be numbered, andmay be arranged in banks, rows, etc. The bank number, row number,element number, etc. associated with the solid-state storage array mayalso then form part of an address scheme. Pages, erase blocks, etc. maybe grouped together to form logical pages, logical erase blocks, etc.

To avoid loss of use of an entire data storage device, a location wherethe data storage device has failed may be noted and marked such thatdata is not stored in the bad location. Often, a region that is markedbad is a block. A bad block table or other data structure may be used toavoid storing data in a bad block. If a particular physical erase blockin a solid-state storage array fails, a logical erase block thatincludes the failed physical erase block may be unavailable unlessanother physical erase block is substituted for the failed physicalerase block. A bad block map is typically used to redirect data reads,writes, etc. from the failed physical erase block in a logical eraseblock being accessed to a replacement physical erase block.

Bad blocks in solid-state storage, such as NAND flash memory, are commonand solid-state storage elements often come from the factory with baderase blocks. Solid-state storage may be used as log storage system andnot as a random access device so bad block mapping schemes developed fordisks and other data storage devices may be inadequate. Solid-statestorage typically also has a wear-out mechanism so areas used frequentlymay be subject to failure before other areas in the solid-state storage.Traditional bad block management techniques are inadequate for providinghighly reliable bad block management for solid-state storage.

SUMMARY

From the foregoing discussion, it should be apparent that a need existsfor an apparatus, system, and method that provide a highly reliable wayto manage bad blocks in solid-state storage. Beneficially, such anapparatus, system, and method would provide a highly reliable, timeefficient bad block management that does not interfere with solid-statestorage performance.

The present invention has been developed in response to the presentstate of the art, and in particular, in response to the problems andneeds in the art that have not yet been fully solved by currentlyavailable bad block mapping systems. Accordingly, the present inventionhas been developed to provide an apparatus, system, and method for badblock remapping that overcome many or all of the above-discussedshortcomings in the art.

The apparatus for bad block remapping is provided with a plurality ofmodules configured to functionally execute the necessary steps ofidentifying one or more data blocks as bad blocks, writing at least alocation of each bad block into each of two or more redundant bad blocklogs, and accessing at least one bad block log during a start-upoperation to create in memory a bad block map. These modules in thedescribed embodiments include a bad block identifier module, a logupdate module, and a bad block mapping module.

The bad block identifier module identifies one or more data blocks asbad blocks. Each bad block includes a block determined to beinappropriate for data storage. Each bad block is on a solid-statestorage element in an array of solid-state storage elements.

The log update module writes at least a location of each bad block (“badblock location”) identified by the bad block identifier module into eachof two or more redundant bad block logs. For at least one of the badblock logs, the log update module writes the one or more bad blocklocations into a page of a block of the bad block log. The page is freeof previously written bad block location information.

The bad block mapping module accesses at least one bad block log duringa start-up operation to create in memory a bad block map. The bad blockmap includes a mapping between the bad block locations in the bad blocklog and a corresponding location of a replacement block (“replacementblock location”) for each bad block location. Data is stored in eachreplacement block instead of the corresponding bad block. The start-upoperation includes making operational a controller for the solid-statestorage from a non-operational state. In one embodiment, the bad blockmapping module creates the bad block map using a replacement blocklocation stored with each bad block location in each of the bad blocklogs. In another embodiment, the bad block mapping module creates thebad block map using a bad block mapping algorithm that uses a storageorder of the bad block locations in a bad block log to pair each badblock location with a replacement block location.

In one embodiment, the apparatus includes a table updater module thatupdates the bad block map by mapping a replacement block location to abad block location. The table updater module stores the mapping in thebad block map. In another embodiment, the apparatus includes a logcompactor module that reads, in a block of a bad block log, each pagestoring one or more bad block locations. The log compactor module alsoerases the pages storing bad block locations and stores at least the badblock locations read from the pages together into one or more pages inthe block of the bad block log (“compacted bad block pages”). In yetanother embodiment, the log compactor module erases pages storing badblock locations and stores the bad block map in one or more pages of theblock that include the bad block log as compacted bad block pages.

In a further embodiment, the log update module, subsequent to the logcompactor module storing bad block locations into the one or morecompacted bad block pages, stores each additional bad block locationcorresponding to a bad block subsequently identified by the bad blockidentifier module. Each additional bad block location is stored in aseparate page and in a page different than the one or more compacted badblock pages.

In a further embodiment, the log compactor module reads one or morecompacted bad block pages and other pages storing a bad block locationand stores the bad block locations in one or more compacted bad blockpages. In another embodiment, the log compactor module reads pages andstores bad block locations in one or more compacted bad block pages inresponse to one or more of reaching a threshold of number of pages withbad block location information and each available page in a bad blocklog having one or more bad block locations.

In one embodiment, the apparatus includes a bad block recovery modulethat recovers valid data stored in an identified bad block and storesthe data in a replacement block mapped to the bad block. The bad blockrecovery module recovers the valid data using error correcting code(“ECC”), a spare die or chip from which the valid data can be covered,or data stored in a stripe of a redundant array of independent drives(“RAID”).

In another embodiment, the apparatus includes a log consistency modulethat compares the two or more bad block logs and, if available, the badblock map and determines if the bad block logs and bad block map areconsistent. In a further embodiment, the log consistency moduledetermines consistency of the bad block logs and bad block map inresponse to one or more of detecting an error while updating one or moreof the bad block logs, the bad block mapping module creating the badblock map during a start-up operation, after an interruption whileupdating the two or more bad block logs, an ECC data correction failure,a periodic scrubbing, expiration of a period of time, and a command by auser.

In a further embodiment, the apparatus includes a log recovery modulethat uses a bad block log that is determined to be correct or the badblock map that is determined to be correct to correct a bad block logthat is determined to be in error. In another embodiment, determiningthat two or more bad block logs are inconsistent includes determiningthat a number of bad block locations in a bad block log or the bad blockmap are different than a number of bad block locations in at least oneother bad block log. In another embodiment, the bad block log with ahigher number of bad block locations is determined to be the bad blocklog with valid bad block location data unless the bad block log with ahigher number of bad block locations is determined to contain invaliddata using ECC checking.

In one embodiment, a replacement block includes a physical block withina retired logical block. The retired logical block includes two or morephysical blocks wherein at least one physical block is a physical blockother than the replacement block and is a bad block. The retired logicalblock also includes a logical block available to store data that ismarked as a retired logical block such that physical blocks in thelogical block are available as replacement blocks.

In another embodiment, a block of a bad block log includes a logicalblock spanning two or more solid-state storage elements wherein ECCprotects the logical block. In another embodiment, the bad block mappingmodule accesses at least one bad block log by accessing the block of thebad block log at a known physical location within the solid-statestorage array. The known physical location includes one of a firstblock, a last block, a block of a predetermined number, and a block at aknown offset into the solid-state storage array.

In one embodiment, the apparatus includes a bad block log replacementmodule that determines that a block that includes a bad block log is ina condition to be replaced, selects a block within a pool of blocksdesignated for bad block data storage, and writes bad block data intothe selected block that is consistent with one of another bad block logand the bad block map. In another embodiment, the log update modulefurther stores one or more of a time indicator and error data with thebad block location. The time indicator includes a point in time or apoint in a sequence. The point in time and point in sequence are eachassociated with identification of the bad block.

In yet another embodiment, a solid-state storage element includes one ofa solid-state storage chip and a solid-state storage die. In oneembodiment, a block is an erase block.

A system of the present invention is also presented for bad blockremapping. The system may be embodied by a solid-state storage arrayincluding two or more solid-state storage elements and a solid-statestorage controller that controls the solid-state storage array. Inparticular, the system, in one embodiment, includes a bad blockidentifier module, a log update module, and a bad block mapping module.The bad block identifier module identifies one or more data blocks asbad blocks. Each bad block includes a block determined to beinappropriate for data storage and each bad block is on a solid-statestorage element in the solid-state storage array.

The log update module writes at least a location of each bad block (“badblock location”) identified by the bad block identifier module into eachof two or more redundant bad block logs. For at least one of the badblock logs the log update module writes the one or more bad blocklocations into a page of a block of the bad block log, where the page isfree of previously written bad block location information.

The bad block mapping module accesses at least one bad block log duringa start-up operation to create in memory a bad block map. The bad blockmap includes a mapping between the bad block locations in the bad blocklog and a corresponding location of a replacement block (“replacementblock location”) for each bad block location. Data is stored in eachreplacement block instead of the corresponding bad block. The start-upoperation includes making operational a controller for the solid-statestorage from a non-operational state. The bad block mapping modulecreates the bad block map using one of a replacement block locationstored with each bad block location in each of the bad block logs and abad block mapping algorithm that uses a storage order of the bad blocklocations in a bad block log to pair each bad block location with areplacement block location. The system, in one embodiment, may furtherinclude a computer that includes the solid-state storage array.

A computer program product comprising a computer readable medium havingcomputer usable program code executable to perform operations is alsopresented for mapping bad blocks in solid-state storage. The computerprogram product includes identifying one or more data blocks as badblocks. Each bad block includes a block determined to be inappropriatefor data storage. Each bad block is on a solid-state storage element inan array of solid-state storage elements. The computer program productalso includes writing at least a location of each identified bad block(“bad block location”) into each of two or more redundant bad blocklogs. For at least one of the bad block logs, the one or more bad blocklocations are written into a page of a block that includes the bad blocklog, where the page is free of previously written bad block locationinformation.

The computer program product includes accessing at least one bad blocklog during a start-up operation to create in memory a bad block map thatincludes a mapping between the bad block locations in the bad block logand a corresponding location of a replacement block (“replacement blocklocation”) for each bad block location. Data is stored in eachreplacement block instead of the corresponding bad block. The start-upoperation includes making operational a controller for the solid-statestorage from a non-operational state. Creating the bad block mapincludes using one of a replacement block location stored with each badblock location in each of the bad block logs and a bad block mappingalgorithm that uses a storage order of the bad block locations in a badblock log to pair each bad block location with a replacement blocklocation.

Reference throughout this specification to features, advantages, orsimilar language does not imply that all of the features and advantagesthat may be realized with the present invention should be or are in anysingle embodiment of the invention. Rather, language referring to thefeatures and advantages is understood to mean that a specific feature,advantage, or characteristic described in connection with an embodimentis included in at least one embodiment of the present invention. Thus,discussion of the features and advantages, and similar language,throughout this specification may, but do not necessarily, refer to thesame embodiment.

Furthermore, the described features, advantages, and characteristics ofthe invention may be combined in any suitable manner in one or moreembodiments. One skilled in the relevant art will recognize that theinvention may be practiced without one or more of the specific featuresor advantages of a particular embodiment. In other instances, additionalfeatures and advantages may be recognized in certain embodiments thatmay not be present in all embodiments of the invention.

These features and advantages of the present invention will become morefully apparent from the following description and appended claims, ormay be learned by the practice of the invention as set forthhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the invention will be readilyunderstood, a more particular description of the invention brieflydescribed above will be rendered by reference to specific embodimentsthat are illustrated in the appended drawings. Understanding that thesedrawings depict only typical embodiments of the invention and are nottherefore to be considered to be limiting of its scope, the inventionwill be described and explained with additional specificity and detailthrough the use of the accompanying drawings, in which:

FIG. 1 is a schematic block diagram illustrating one embodiment of asystem for mapping bad blocks in solid-state storage in accordance withthe present invention;

FIG. 2 is a schematic block diagram illustrating one embodiment of anapparatus for mapping bad blocks in solid-state storage in accordancewith the present invention;

FIG. 3 is a schematic block diagram illustrating another embodiment ofan apparatus for mapping bad blocks in solid-state storage in accordancewith the present invention;

FIG. 4 is a schematic flow chart diagram illustrating one embodiment ofa method for mapping bad blocks in solid-state storage in accordancewith the present invention;

FIG. 5 is a schematic flow chart diagram illustrating another embodimentof a method for mapping bad blocks in solid-state storage in accordancewith the present invention;

FIG. 6 is a schematic flow chart diagram illustrating one embodiment ofa method for detecting and replacing a bad block log in solid-statestorage in accordance with the present invention;

FIG. 7 is a schematic block diagram illustrating one embodiment of anarray of solid-state storage devices depicting blocks in the array inaccordance with the present invention; and

FIG. 8 is a schematic block diagram illustrating one embodiment of anarray of solid-state storage devices depicting pages in a block in thearray in accordance with the present invention.

DETAILED DESCRIPTION

Many of the functional units described in this specification have beenlabeled as modules, in order to more particularly emphasize theirimplementation independence. For example, a module may be implemented asa hardware circuit comprising custom VLSI circuits or gate arrays,off-the-shelf semiconductors such as logic chips, transistors, or otherdiscrete components. A module may also be implemented in programmablehardware devices such as field programmable gate arrays, programmablearray logic, programmable logic devices or the like.

Modules may also be implemented in software for execution by varioustypes of processors. An identified module of executable code may, forinstance, comprise one or more physical or logical blocks of computerinstructions which may, for instance, be organized as an object,procedure, or function. Nevertheless, the executables of an identifiedmodule need not be physically located together, but may comprisedisparate instructions stored in different locations which, when joinedlogically together, comprise the module and achieve the stated purposefor the module.

Indeed, a module of executable code may be a single instruction, or manyinstructions, and may even be distributed over several different codesegments, among different programs, and across several memory devices.Similarly, operational data may be identified and illustrated hereinwithin modules, and may be embodied in any suitable form and organizedwithin any suitable type of data structure. The operational data may becollected as a single data set, or may be distributed over differentlocations including over different storage devices, and may exist, atleast partially, merely as electronic signals on a system or network.Where a module or portions of a module are implemented in software, thesoftware portions are stored on one or more computer readable media.

Reference throughout this specification to “one embodiment,” “anembodiment,” or similar language means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment of the present invention. Thus,appearances of the phrases “in one embodiment,” “in an embodiment,” andsimilar language throughout this specification may, but do notnecessarily, all refer to the same embodiment.

Reference to a computer readable medium may take any form capable ofstoring machine-readable instructions on a digital processing apparatus.A computer readable medium may be embodied by a transmission line, acompact disk, digital-video disk, a magnetic tape, a Bernoulli drive, amagnetic disk, a punch card, flash memory, integrated circuits, or otherdigital processing apparatus memory device.

Furthermore, the described features, structures, or characteristics ofthe invention may be combined in any suitable manner in one or moreembodiments. In the following description, numerous specific details areprovided, such as examples of programming, software modules, userselections, network transactions, database queries, database structures,hardware modules, hardware circuits, hardware chips, etc., to provide athorough understanding of embodiments of the invention. One skilled inthe relevant art will recognize, however, that the invention may bepracticed without one or more of the specific details, or with othermethods, components, materials, and so forth. In other instances,well-known structures, materials, or operations are not shown ordescribed in detail to avoid obscuring aspects of the invention.

The schematic flow chart diagrams included herein are generally setforth as logical flow chart diagrams. As such, the depicted order andlabeled steps are indicative of one embodiment of the presented method.Other steps and methods may be conceived that are equivalent infunction, logic, or effect to one or more steps, or portions thereof, ofthe illustrated method. Additionally, the format and symbols employedare provided to explain the logical steps of the method and areunderstood not to limit the scope of the method. Although various arrowtypes and line types may be employed in the flow chart diagrams, theyare understood not to limit the scope of the corresponding method.Indeed, some arrows or other connectors may be used to indicate only thelogical flow of the method. For instance, an arrow may indicate awaiting or monitoring period of unspecified duration between enumeratedsteps of the depicted method. Additionally, the order in which aparticular method occurs may or may not strictly adhere to the order ofthe corresponding steps shown.

In solid state storage, such as flash, it is not uncommon for arrays ofmemory to come from the factory with bad blocks. It is common practicefor the first page of each erase block in these devices to come with badblock information for the array (hereafter, “block” is equivalent to“erase block”). While vendors usually guarantee that block zero is good,we have found this to sometimes not be the case. The cost of rework issufficiently high that it is desirable to continue to operate the devicewhen block zero is found bad or goes bad during the life of the product.

During the manufacturing process, we have found it to be good practiceto read and store this bad block information for the entire array ofchips within a solid state storage device, and then scrub the entiredevice to verify that there are no additional bad blocks. Then typicallythe bad block information from the factory is merged with the bad blockdata identified during the scrubbing process and programmed back intothe device. The bad block information is typically stored in aconsolidated format, which may be a table. This consolidated bad blocktable is typically more efficient to use and maintain than having badblock data spread out. This consolidated bad block data structure has anadditional benefit of returning pages reserved for bad block informationto be used to increase capacity for later bad block information.

The storage device typically maintains a table or other data structureof LEB (Logical Erase Block) to PEB (Physical Erase Block) mappings.This enables higher layers of software controlling and accessing thesolid-state storage to address LEBs directly typically without concernfor the underlying PEB layout, even given the fact that numerous PEBsmay have failed on typical NAND parts. Because this information must bepersistent, in one embodiment, this information is redundantly stored innon-volatile memory in two or more distinct erase blocks. In addition,the bad block information is preferably protected with a robust errorcorrecting code (“ECC”) and may also be protected using a spare chip ordie in a scheme where that data in a bad block can be recovered.

Bad block information, which includes a bad block location, is oftenstored as tuples comprising the die and bad erase block, although it maybe stored as an address, or other way that indicates location. Whenadditional blocks fail during operation of the part, informationregarding the additional bad block location is typically appended to alist, map, etc. of bad blocks.

Since this bad block location data is critical to the operation of thedevice, and the loss of the bad block information might cause futureoperation of the solid-state storage device to lose and/or corrupt data,it is advisable to store multiple copies of the bad block data. Storingmultiple copies of the bad block data has an additional benefit ofincreasing the probability that a failure to program one blockcontaining the bad block information with one or more additional tuplesor other form of bad block location data does not risk loss of the badblock data. It is preferable to store the redundant information inseparate erase blocks, and more preferable yet to store the redundantbad block data in an entirely separate area of the non-volatile storageas compared to storing multiple instances of the bad block data inadjacent cells.

Another means to reduce the probability of failure of the blockscontaining the bad block location data is to reduce the wear on theseblocks. In one embodiment, this is done by programming one or more newfailed block locations into a next available page. While this may beseen as a waste of space, saving additional bad block locations in anext available page avoids having to do multiple page programs—whichtypically should be avoided due to the negative impacts to thereliability of the data. Saving additional bad block locations in a nextavailable page also avoids having to read out bad block locations fromthe block storing the bad block data, erase the block storing the badblock data, merge the new bad block location data into the list of badblocks, and then program the list back to the block storing the badblock data. While such a process might have limited negative impact onthe life of the part, more importantly, it is not time efficient.

During a scrubbing process, for example when a die is received from afactory, two or more erase blocks are typically identified to hold thebad block data. These blocks are typically uniquely identified with aspecific erase block header stored within the blocks. While block zerowould usually be one of these, this need not be the case. These blocksfor storing bad block data may be taken from a predetermined pool ofblocks that is a minor subset of a total number of blocks in asolid-state storage array. This facilitates finding the blocks storingbad block data immediately following the reset of the solid-statestorage device. Said differently, whereas the controller for thesolid-state storage must access these blocks in order to build a badblock remap table, which is typically needed in advance of accessing anydata on the device, it is typically requisite to first scan thesolid-state storage device and identify these blocks storing bad blockdata and load the bad block information into the bad block remap tablein whatever form that may take.

To further reduce the time needed to identify these blocks storing badblock data, each of the blocks may additionally include the address ofthe one or more redundant blocks containing bad block data. This hasadditional benefit of helping to validate that the correct blocksstoring bad block data have been identified.

As mentioned previously, new bad block tuples or bad block locations areprogrammed into a next available empty page. At a prescribed point, whenthe device is close to running out of pages to append additional tuples,has reached a threshold of number of pages with bad block data, or someother trigger, one of the blocks may be erased, the tuples or bad blocklocations consolidated, and the bad block list, map, or other structureis written back into the block with bad block data along with headerinformation and the one or more peer block identifiers. A peer block isan additional block that stores redundant bad block data. Oncecompleted, the other blocks can be erased and consolidated.

In the event that there is a power outage while one of these blocks isbeing updated, in one embodiment the solid-state storage controller willbe able to identify the block with the most bad block data as the mostcurrent copy. The process of completing updates of the one or more peerblocks then takes place.

The bad block remapping tables or other data structure with bad blockdata used by the controller, in one embodiment, are built from the listof bad blocks through a predetermined bad block mapping algorithm thatdeterministically remaps the bad blocks per the order of the tuples orbad block locations in the list. In this embodiment, it is importanttherefore that the list of tuples not be reordered. Generally these badblock tables are maintained in random access memory (“RAM”). Generally,these bad block tables are not stored in non-volatile memory, due tosize constraints, and the fact that they can be efficientlyreconstructed from a bad block log. A bad block log comprises bad blocklocation data and other data, such as corresponding replacement block,stored in a block of a known location. This scheme uses a relatively lowamount of non-volatile memory capacity to store the bad block list andthe implicit bad block remapping.

In one embodiment, other data may be stored with bad block data. For anewly identified bad block, for example, a time indicator may be stored.A time indicator is typically some indicator of time or sequence thatties bad block identification with a time or sequence. For example, thetime indicator may be a timestamp, a value from a block sequencecounter, or the like. Storage of a time indicator, among other benefits,enables tracking of a rate at which bad blocks are identified, which mayhelp determine a rate of wear out and expected life of the solid-statestorage. In addition, other data may also be stored with bad block data,such as error data indicating an error type or some other indication oferror associated with identification of the bad block.

In another embodiment, the bad block tuples or locations are storedalong with replacement block data such a replacement block location.This might be done to enable hardware to access the bad block mappingwithout having to execute the bad block mapping algorithm. In this case,the tuples might be reordered. Here, the order might be maintained sothat a scrubber might read the list and validate that the remapping isconsistent. A scrubber might additionally validate the bad block data bycomparing the blocks containing the bad block data.

As implied above, generally, the bad block remap table or data structurewill be loaded into RAM, for fast access. The previously mentionedschemes for identifying the bad blocks and the remapping of the badblocks are typically loaded into the RAM during device initialization orother instance when the bad block map is corrupted or lost. In oneembodiment, bad block information stored in RAM differs from how thesame bad block information is stored in non-volatile memory. In anotherembodiment, bad block information is stored in RAM in a same format asthe bad block information is stored in non-volatile memory.

If one of the blocks fails during the life of the product, another blockis selected from the previously mentioned pool of blocks set aside forbad block data, and the data is copied from the at least one peer(redundant bad block log) to the new block. The new block is initializedwith header information and peer address information. The peers are thenupdated with the information of the new block with the bad block log,such as the address of the new block. In one embodiment, each peer blockis erased and updated, and typically bad block information isconsolidated before being stored back to a peer block. In a preferredembodiment, bad block information from a peer block is also stored in aconsolidated form to the new, replacement block storing bad blockinformation. In a preferred embodiment, a record of the change iswritten into the next available page within the block with bad blockdata. This embodiment typically requires any code attempting todetermine a peer to read the entire block to ensure that the peerinformation in the first page of the block is not stale.

FIG. 1 is a schematic block diagram illustrating one embodiment of asystem 100 for mapping bad blocks in solid-state storage 106 inaccordance with the present invention. The system 100 includes asolid-state storage device 102 with a solid-state controller 104 andsolid-state storage 106. In one embodiment, the solid-state storagedevice 102 is in a computer 108 connected to one or more clients 110through a computer network 112. The system 100 includes a bad blockmapping apparatus 114. The components of the system 100 are describedbelow.

The system 100 includes at least one solid-state storage device 102. Inanother embodiment, the system 100 includes two or more solid-statestorage devices 102. Each solid-state storage device 102 may includenon-volatile, solid-state storage 106, such as flash memory, nano randomaccess memory (“nano RAM or NRAM”), magneto-resistive RAM (“MRAM”),dynamic RAM (“DRAM”), phase change RAM (“PRAM”), etc. The solid-statestorage device 102 is depicted in a computer 108 connected to a client110 through a computer network 112. In one embodiment, the solid-statestorage device 102 is internal to the computer 108 and is connectedusing a system bus, such as a peripheral component interconnect express(“PCI-e”) bus, a Serial Advanced Technology Attachment (“serial ATA”)bus, or the like.

In another embodiment, the solid-state storage device 102 is external tothe computer 108 and is connected, a universal serial bus (“USB”)connection, an Institute of Electrical and Electronics Engineers(“IEEE”) 1394 bus (“FireWire”), or the like. In other embodiments, thesolid-state storage device 102 is connected to the computer 108 using aperipheral component interconnect (“PCI”) express bus using externalelectrical or optical bus extension or bus networking solution such asInfiniband or PCI Express Advanced Switching (“PCIe-AS”), or the like.

In various embodiments, the solid-state storage device 102 may be in theform of a dual-inline memory module (“DIMM”), a daughter card, or amicro-module. In another embodiment, the solid-state storage device 102is an element within a rack-mounted blade. In another embodiment, thesolid state storage device 102 is contained within a package that isintegrated directly onto a higher level assembly (e.g. mother board, laptop, graphics processor). In another embodiment, individual componentscomprising the solid-state storage device 102 are integrated directlyonto a higher level assembly without intermediate packaging.

The solid-state storage device 102 includes one or more solid-statestorage controllers 104, each may include a write data pipeline and aread data pipeline and each includes a solid-state storage 106. Thesolid-state storage 106 comprises two or more solid-state storageelements, such as a solid-state storage chip or die. The solid-statestorage 106 may be arranged with multiple solid-state storage elementsin a bank and may have two or more banks. The solid-state storage 106,write data pipeline, read data pipeline, and other relevant componentsis described in detail in U.S. patent application Ser. No. 11/952,091 toDavid Flynn, et al., titled “Apparatus, System, and Method for ManagingData Using a Data Pipeline,” filed Dec. 6, 2007, which is hereinafterincorporated by reference.

The system 100 includes one or more computers 108 connected to thesolid-state storage device 102. A computer 108 may be a host, a server,a storage controller of a storage area network (“SAN”), a workstation, apersonal computer, a laptop computer, a handheld computer, asupercomputer, a computer cluster, a network switch, router, orappliance, a database or storage appliance, a data acquisition or datacapture system, a diagnostic system, a test system, a robot, a portableelectronic device, a wireless device, or the like. In anotherembodiment, a computer 108 may be a client and the solid-state storagedevice 102 operates autonomously to service data requests sent from thecomputer 108. In this embodiment, the computer 108 and solid-statestorage device 102 may be connected using a computer network, systembus, or other communication means suitable for connection between acomputer 108 and an autonomous solid-state storage device 102. One ofskill in the art will recognize other forms of a computer 108 and waysto connect the solid-state storage device 108 through a computer networkor bus.

In one embodiment, the system 100 includes one or more clients 110connected to one or more computers 108 through one or more computernetworks 112. A client 110 may be a host, a server, a storage controllerof a SAN, a workstation, a personal computer, a laptop computer, ahandheld computer, a supercomputer, a computer cluster, a networkswitch, router, or appliance, a database or storage appliance, a dataacquisition or data capture system, a diagnostic system, a test system,a robot, a portable electronic device, a wireless device, or the like.The computer network 112 may include the Internet, a wide area network(“WAN”), a metropolitan area network (“MAN”), a local area network(“LAN”), a token ring, a wireless network, a fiber channel network, aSAN, network attached storage (“NAS”), ESCON, or the like, or anycombination of networks. The computer network 112 may also include anetwork from the IEEE 802 family of network technologies, such Ethernet,token ring, WiFi, WiMax, and the like. One of skill in the art willrecognize other forms of a client 110 and other computer networks 112.

The computer network 112 may include servers, switches, routers,cabling, radios, and other equipment used to facilitate networkingcomputers 108 and clients 110. In one embodiment, the system 100includes multiple computers 108 that communicate as peers over acomputer network 112. In another embodiment, the system 100 includesmultiple solid-state storage devices 102 that communicate as peers overa computer network 112. One of skill in the art will recognize othercomputer networks 112 comprising one or more computer networks 112 andrelated equipment with single or redundant connection between one ormore clients 110 or other computer with one or more solid-state storagedevices 102 or one or more solid-state storage devices 102 connected toone or more computers 108. In one embodiment, the system 100 includestwo or more solid-state storage devices 102 connected through thecomputer network 118 to a client 112 without a computer 108.

The system 100 includes a bad block mapping apparatus 114. The bad blockmapping apparatus 114 is depicted in FIG. 1 in the solid-state storagedevice 102, but may be in the solid-state controller 104, solid-statestorage 106, computer 108, etc. The bad block mapping apparatus 114 maybe located together or distributed. One of skill in the art willrecognize other forms of a bad block mapping apparatus 114. The badblock mapping apparatus 114 is described in more detail below.

FIG. 2 is a schematic block diagram illustrating one embodiment of anapparatus 200 for mapping bad blocks in solid-state storage 106 inaccordance with the present invention. The apparatus 200 includes oneembodiment, of the bad block mapping apparatus 114 and includes, in oneembodiment, a bad block identifier module 202, a log update module 204,and a bad block mapping module 206, which are described below.

In one embodiment, apparatus 200 includes a bad block identifier module202 that identifies one or more data blocks as bad blocks. Each badblock is located on a solid-state storage element in an array ofsolid-state storage elements 106. Each data block, and hence bad block,typically is a physical block. In one embodiment, a physical block is aphysical erase block (“PEB”). An erase block is typically a block thatis erased in an erase operation. In another embodiment, a physical blockis not an erase block, but is independent of a unit of storage erased inan erase operation. A physical erase block is typically an erase blocklocated on one die, chip, or other solid-state storage element thatcomprises an element of the solid-state storage array. (The solid-statestorage array is shown in FIG. 1 as the solid-state storage 106 and theterms may be used interchangeably herein.)

A PEB typically includes multiple pages and a page is typically a groupof bytes that are programmed together. In one embodiment, a group ofPEBs forms a logical erase block (“LEB”). A page in each PEB may form alogical page and a logical page may be programmed together. For example,a write buffer, when filled, may be written to a logical page. In apreferred embodiment, a logical page is protected together with ECC andforms an ECC chunk. In one embodiment, an ECC chunk may be arranged toprotect a bad block log as well as other data. While an array ofsolid-state storage elements is preferred, it is contemplated that theinvention described herein also applies to a solid-state storage elementand therefore “block” may include a single block or a logical block. Forexample, a bad block is typically a bad PEB while a block storing badblock data is typically a logical block spanning multiple solid-statestorage elements.

Each bad block is a block determined to be inappropriate for datastorage. For example, a bad block may include a page or other portion ofthe block that has failed in some way. For example, a bad block mayinclude bits that are stuck, a faulty address line, a faulty pageselection line, etc. or a number of errors above a threshold. The errorsmay be recoverable errors or non-recoverable errors. In one embodiment,the bad block identifier module 202 receives information from a die orchip that an erase or a program has not completed correctly, which isinterpreted as an indication of a bad block. This indication is a commonsignal available on NAND flash devices.

For example a bad block may be a block with one or more non-recoverableerrors. A non-recoverable error may include an error that is notcorrectable using ECC protecting data in the bad block. One of skill inthe art will recognize other ways to determine a non-recoverable error.In another embodiment, the bad block identifier module 202 may identifya bad block using a scrubbing process, device initialization, errorchecking, or other way to find a bad block that will not functionproperly to reliably store data.

In one embodiment, a bad block may be a block may be functional but thathas an increased number of correctable errors. For example, a bad blockmay be a block with a number of correctable errors above a threshold. Inanother example, a bad block may be a block with a high number of readsor writes. One of skill in the art will recognize other ways todetermine if a bad block is no longer suitable for storing data. The badblock identifier module 202 may include any method that identifies ablock that is not suitable for storing data.

In one embodiment, the apparatus 200 includes a log update module 204that writes at least a location of each bad block (“bad block location”)identified by the bad block identifier module 202 into each of two ormore redundant bad block logs. As mentioned above, a bad block log is alocation in a block that includes bad block data. A bad block log may bea tuple, a table, a data field, or other data structure that allows abad block location and any other relevant data, such as a replacementblock location to be stored in a designated block. Typically, the badblock log is stored in a logical block spanning a bank of solid-statestorage elements in the solid-state storage 106 and protected by ECC foreach a logical page in the logical block. In one embodiment, the logicalblock storing the bad block data may span all banks. In anotherembodiment, this same logical block may span all channels.

For at least one of the bad block logs (and typically all of the badblock logs), the log update module 204 writes the one or more bad blocklocations into a page of a block comprising the bad block log where thepage does not have previously written bad block location information. Asstated above, by writing the one or more new bad block locations of badblocks identified by the bad block identifier module 202, recording thebad block data is more efficient and is faster than reading the badblock log, modifying the bad block data stored in the bad block log,erasing the pages storing the bad block data, and then writing theupdated bad block data back to a block designated to store the bad blocklog. It is also faster than modifying the bad block data and thenstoring the modified bad block data into the next available page withinthe erase block.

Writing updated bad block data to a new page offers significantadvantages over conventional bad block management methods. In oneembodiment, when a bad block is identified, the bad block location andother pertinent data that may be used to update a bad block map isconfigured as a delta file that includes a difference between an updatedversion of the bad block map and a version of the bad block map beforethe update. The log update module 204, in this embodiment, stores thedelta file in a new page. Writing bad block data to a new page andsubsequent compaction will be described in more detail with respect toFIG. 3.

In one embodiment, the bad block mapping apparatus 114 includes a badblock mapping module 206 that accesses at least one bad block log duringa start-up operation to create in memory a bad block map. The bad blockmap includes a mapping between the bad block locations in the bad blocklog and a corresponding location of a replacement block (“replacementblock location”) for each bad block location. Data is stored in eachreplacement block instead of the corresponding bad block.

Typically a replacement block is a physical block or PEB within aretired logical block or retired LEB. In one embodiment a retiredlogical block has two or more physical blocks where at least onephysical block is a bad block determined to be bad at a previous time,thus making available physical blocks in the logical block other thanthe bad block to be used as a replacement block. In another embodiment,a logical block that is in a pool of logical blocks available for datastorage is retired, thus making available all of the physical blocks inthe logical block to become replacement blocks.

The start-up operation includes making operational the solid-statestorage controller 104 from a non-operational state. The start-upoperation may include starting up the solid-state storage controller 104when power is applied, when resuming operation after being in alow-power state, after a reset, etc. The start-up operation includes anycircumstance where the bad block map must be stored in memory. Such acircumstance includes any state where the memory is corrupted or lost.The memory is typically RAM and may include any level of cache. One ofskill in the art will recognize when the bad block map must be createdin memory.

There are multiple ways that the bad block mapping module 206 may createthe bad block map. For example in a preferred embodiment, a replacementblock location is stored with a corresponding bad block location in oneor more bad block logs. Typically a replacement block chosen to replacea bad block is a different physical block than the bad block but thereplacement block is typically within the same die or chip. Selecting areplacement block on a same die or chip as a bad block is preferred overselection of a replacement block in another die, chip, bank, etc.because a more complicated address scheme would typically be required,such as multiplexing (“MUXing”). In this embodiment, the bad blockmapping module 206 may create the bad block map using the replacementblock location stored with each bad block location. In this embodiment,the order of storage of the bad block locations may not be required tobuild the bad block map but may instead be useful for determiningconsistency between the bad block logs.

In another embodiment, the bad block map is stored in one or more of thebad block logs and the bad block mapping module 206 may build the badblock map by reading a bad block log. In another embodiment bad blocklocations are stored in a particular order in the bad block logs and thebad block mapping module creates a bad block map using a bad blockmapping algorithm that uses a storage order of the bad block locationsin a bad block log to pair each bad block location with a replacementblock location. For example, the bad block mapping algorithm may, inthis embodiment, pair a first bad block location with a firstreplacement block, the second bad block location with a secondreplacement block, etc. where the replacement block locations and orderare determined algorithmically. In one embodiment, the bad block mapdiffers from bad block data stored in a bad block log.

In one embodiment, a bad block data may be stored as a bit map, whichtypically may be a sparse bit map. This sparse bit map might be coupledwith a corresponding replacement map to allow for more compact, andrapid lookup of bad block data. One of skill in the art will recognizeother ways that the bad block mapping module 206 may create a bad blockmap from bad block location stored in a bad block log.

Typically the bad block mapping module 206 accesses at least one badblock log by accessing the block comprising the bad block log at a knownphysical location within the solid-state storage array 106. Having thebad block log in a block with a known physical location allows a bios orother startup code to access the bad block log with a simple directaddress. The known physical location may be a first block, a last block,a block of a predetermined number, a block at a known offset into thesolid-state storage array, etc.

FIG. 3 is a schematic block diagram illustrating another embodiment ofan apparatus 300 for mapping bad blocks in solid-state storage 106 inaccordance with the present invention. The apparatus 300 includes analternate bad block mapping apparatus 114 with a bad block identifiermodule 202, a log update module 204, and a bad block mapping module 206,which are substantially similar to those described with respect to theapparatus 200 in FIG. 2. The apparatus 300, in various embodiments, mayalso include a table updater module 302, a log compactor module 304, abad block recovery module 306, a log consistency module 308, a logrecovery module 310, and a bad block log replacement module 312, whichare described below.

The apparatus 300, in one embodiment, includes a table updater module302 that updates the bad block map by mapping a replacement blocklocation to a bad block location and then storing the mapping in the badblock map. Typically the table updater module 302 updates the bad blockmap after the bad block identifier module 202 identifies a bad block. Inone embodiment, the table updater module 302 starts with an empty badblock map and updates the bad block map with factory bad blocklocations. The table updater module 302 may then add to the bad blockmap during a scrubbing operation where storage locations in thesolid-state storage 106 are tested. In another embodiment, the tableupdater module 302 updates the bad block map after a failure of at leasta portion of a bad block and the bad block identifier module 202identifies the failed bad block. One of skill in the art will recognizeother times when the table updater module 302 may update the bad blockmap.

The bad block map may be a table, a linked list, or other data structurethat allows bad block locations to be paired with replacement blocklocations. The bad block map may be stand alone structure or may be partof a logical-to-physical map or other data structure. One of skill inthe art will recognize other ways to structure a bad block map.

In another embodiment, the apparatus 300 includes a log compactor module304. Typically the log compactor module consolidates bad block locationsand related data in various pages in a bad block log. In one embodimentthe log compactor module 304 reads a block comprising a bad block logand reads each subsequent page storing one or more bad block locations.If the log update module 204 stores bad block locations in a new pageeach time the bad block identifier module 202 identifies a bad block,each page may be sparsely populated with bad block data. The log updatemodule 204 may also store other system information that may be used at alater time by management. For example, the log update module 204 maystore a time stamp, an error code, etc.

In the embodiment, the log compactor module 304 typically erases thepages storing bad block locations and stores at least the bad blocklocations read from the pages together into one or more pages in theblock comprising the bad block log (“compacted bad block pages”). In atypical embodiment, the pages with bad block data are logical pages. Thelog compactor module 304 erases the bad block data before storage toprevent possible conflicts with the compacted bad block data stored backto the block with the bad block log.

Typically the block with the bad block log includes 64 pages and whenbad block data is compacted, it will fit in a single logical page.Subsequent bad block locations are then stored each in a new page. Asthe block fills again with pages with bad block data, the log compactormodule 304 may again compact the bad block data in a first page wherecompacted bad block data was previously stored or in a second logicalpage. This process may then repeat.

In another embodiment, the log compactor module 304 erases pages storingbad block locations and stores the bad block map in one or more pages ofthe block comprising the bad block log. The log compactor module 304stores the bad block map as one or more compacted bad block pages.Subsequently the log update module 204 stores additional bad blocklocations in new pages as with the example above and the log compactormodule 304 may again at some point store the bad block map in the badblock log and then start the process over again.

The log compactor module 304 may compact the bad block log when theblock is full of pages with bad block data, may compact the bad blocklog when reaching a threshold of number of pages with bad block locationinformation, or some other triggering action known to those of skill inthe art. The log compactor module 304 may also consolidate other datastored in conjunction with the bad block map into respective logs orcause the information to be communicated to an external managementsystem. For example, management data would be consolidated into amanagement log simultaneously to the consolidation of the bad block log.

In another embodiment, the apparatus 300 includes a bad block recoverymodule 306 that recovers valid data stored in an identified bad blockand stores the data in a replacement block mapped to the bad block. Thebad block recovery module 306 may recover the valid data in any numberof ways. In one example, if the identified bad block is stillfunctioning, but is merely demonstrating degraded operation, isexperiencing recoverable errors, the bad block recovery module 306 mayrecover the data directly from the bad block. In another embodiment, thevalid data in the bad block may be unavailable so the bad block recoverymodule 306 may use ECC to correct data read from the bad block, may readvalid data derived from a spare chip or die, may recreate the valid datastored in a stripe of a redundant array of independent drives (“RAID”),may read data from a mirror, or may use another data recovery method.

The apparatus 300, in one embodiment, includes a log consistency module308 that compares the two or more bad block logs and, if available, thebad block map and determines if the bad block logs and bad block map areconsistent. Typically the bad block map and bad block logs areconsistent if they all reflect the same bad block data even if indifferent forms. If one of the bad block logs or the bad block map isinconsistent, in a preferred embodiment a voting scheme may be used andtwo or more of the total number of bad block logs or the bad block mapthat are correct may be used to fix the inconsistent log or map.Typically a bad block log or a bad block map that is determined to becorrect can be used to correct an inconsistent bad block log or map.

In a simple example if power is lost or some similar event occurs whilethe log update module 204 is updating a bad block log or the bad blockmapping module 206 is updating the bad block map, the number of badblock locations in each of the bad block logs and bad block may bedifferent, which typically indicates an inconsistency. In this case, thelog consistency module 308 may determine that a log is inconsistent ifit has less bad block locations than other bad block logs or the badblock map and the bad block logs or map that has the most bad blocklocations can be used to update the bad block logs or map that areinconsistent. However, if the bad block logs or map with more bad blocklocations is determined to have an error through ECC checking or othermeans, then the bad block log or map may still be inconsistent.

The log consistency module 308 may determine consistency based on anumber of triggering events, such as detecting an error while updatingone or more of the bad block logs, the bad block mapping module 206creating the bad block map during a start-up operation, after aninterruption while updating the two or more bad block logs, afterdetermining that ECC cannot correct errors in data, in response to aperiodic scrubbing operation, expiration of a period of time, ascommanded by a user, etc. One of skill in the art will recognize otherways that the log consistency module 308 may commence checking ofconsistency of bad block logs and/or a bad block map.

In one embodiment, the apparatus 300 includes a bad block logreplacement module 312 that corrects a situation where a bad block logis in a block that is defective, is unreadable, has failed, is about tofail, etc. The bad block log replacement module 312 first determinesthat a block that includes a bad block log is in a condition to bereplaced. The bad block log replacement module 312 then selects a blockwithin a pool of blocks designated for bad block data storage and thewrites bad block data into the selected block that is consistent withanother bad block log and/or the bad block map. Having a designated poolof blocks designated to store bad block logs is advantageous because thedesignated blocks may remain unused until designated to store bad blockdata, thus reducing wear and increasing reliability.

FIG. 4 is a schematic flow chart diagram illustrating one embodiment ofa method 400 for mapping bad blocks in solid-state storage 106 inaccordance with the present invention. The method 400 begins and the badblock identifier module 202 identifies 402 one or more data blocks asbad blocks. This may occur by reading factory bad block data, during ascrubbing operation, during normal operation of the solid-state storage106 when a block fails, has errors, has a high number of reads, etc., orother situation where a bad block may be identified.

The bad block mapping module 206 accesses 404 at least one bad block logduring a start-up operation to create a bad block map in memory. The badblock map includes a mapping between the bad block locations in the badblock log and a corresponding location of a replacement block for eachbad block location. Data is stored in each replacement block instead ofthe corresponding bad block.

The log update module 204 writes 406 at least a location of each badblock identified by the bad block identifier module 202 into each of twoor more redundant bad block logs and the method 400 ends. Typically thebad block location is stored in a new page in each block containing abad block log. The log update module 204 may write 406 bad block datainto a bad block log during a scrubbing operation, normal operation, andthe like.

FIG. 5 is a schematic flow chart diagram illustrating another embodimentof a method 500 for mapping bad blocks in solid-state storage inaccordance with the present invention. The method 500 begins and the badblock mapping module 206 accesses 502 at least one bad block log duringa start-up operation to create a bad block map in memory. This may occurafter a reset, during a scrubbing operation, etc.

The bad block identifier module 202 identifies 504 one or more datablocks as bad blocks and the log update module 204 writes 506 at least alocation of each bad block identified by the bad block identifier module202 into each of two or more redundant bad block logs in a new page. Thetable updater module 302 updates 508 the bad block map in memory withthe new bad block location identified 504 by the bad block identifiermodule 202.

The bad block recovery module 306 recovers 510 valid data stored in thebad block using ECC, RAID, a minor, etc. and stores 510 the valid datain the replacement block. The log compactor module 304 determines 512 ifa page limit in the block comprising the bad block log has been reached.If the log compactor module 304 determines 512 that a page limit in theblock comprising the bad block log has been reached, the log compactormodule 304 reads the bad block log, erases the bad block data in the badblock log, and compacts 514 bad block location data and other data intoa single page, and the method 500 ends. If the log compactor module 304determines 512 that a page limit in the block comprising the bad blocklog has not been reached, the method 500 ends.

Note that the steps of the method are only one embodiment and one ormore of the steps may occur during a scrubbing operation, a factorystartup operation, startup, normal operation, etc. The steps may occurin any order and FIG. 5 merely depicts one order of operation.

FIG. 6 is a schematic flow chart diagram illustrating one embodiment ofa method 600 for detecting and replacing a bad block log in solid-statestorage in accordance with the present invention. The method 600 beginsand the log consistency module 308 compares 602 bad block logs and thebad block map, if the map is available, to determine 604 if the badblock logs and map are consistent. If the log consistency module 308determines 604 that the bad block logs and map are consistent, themethod 600 ends.

In this particular embodiment, determining 604 that a bad block log isinconsistent signifies that the block containing the bad block log hasfailed or is otherwise non-operational. In this case, the bad block logreplacement module 312 selects 606 a block within a pool of blocksdesignated for bad block data storage. In another embodiment, the badblock log may be inconsistent for another reason, such as a power outagewhile the bad block log was being updated, so step 606 is skipped. Thelog recovery module 310 uses data from a bad block log that isdetermined to be correct or the bad block map that is determined to becorrect and writes 608 correct bad block data into the bad block log andthe method 600 ends.

FIG. 7 is a schematic block diagram illustrating one embodiment 700 ofan array of solid-state storage devices 106 depicting blocks in thearray in accordance with the present invention. The solid-state storagearray 106 includes several solid-state storage elements 702 a, 702 b, .. . 702 n. Each solid state storage element 702 includes m blocks. Forexample, solid-state storage element 1 702 a includes block 0 704 a,block 1 706 b, block 2708 a, block 3 710 a, block 4 712 a, . . . block m714 a. Logical block 0 716 includes each block 0 704 from eachsolid-state storage element 702. Logical block 0 716 may be designatedfor bad block data storage.

In this example, logical block 2 718 has a failure in physical block 2708 c in solid-state storage element 3 702 c. Logical block 4 720, inthis embodiment, was used for storing data and experienced a failure inphysical block 4 712 b within solid-state storage element 2 702 b and isdesignated as a retired block. The physical block 4 712 c in solid-statestorage element 3 702 c may then be used as a replacement block for badphysical block 2 708 c in solid-state storage element 3 702 c.

FIG. 8 is a schematic block diagram illustrating one embodiment 800 ofan array of solid-state storage devices depicting pages in a block inthe array in accordance with the present invention. The embodiment 800depicts a single block 0 for solid-state storage elements 1-n 702 a-n.Each block 0 704 includes p pages, e.g. page 0 802, page 1 804, page 2806, . . . page p 808. In one embodiment, block 0 704 is used to storebad block data.

If page 0 802 has bad block data, either compressed or uncompressed,after the bad block identifier module 202 identifies a bad block, thelog updater module 204 updates the bad block log by writing the badblock location and possibly other relevant data, such as a replacementblock location, into the next logical page, which is logical page 1 810.The process repeats for page 2 806, page 3, etc. In one embodiment, whenpage p 808 is written to with bad block data, the log compactor module304 may compact the bad block data into one of the pages, such as page 0802.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed is:
 1. An apparatus to map bad blocks in solid-statestorage, the apparatus comprising: a bad block identifier module toidentify at least one physical block as a bad block, wherein the atleast one physical block is associated with a plurality of physicalblocks within a first logical block in an array of solid-state storageelements; and a log update module to store bad block informationassociated with the bad block in a page of a second logical block in thearray of solid-state storage elements, wherein the bad block informationcomprises a location of the bad block in the first logical block, andwherein the second logical block is different from the first logicalblock; wherein the apparatus is further configured to: identify at leastone page previously reserved for storing bad block information in thefirst logical block; and return the at least one page previouslyreserved for storing bad block information to the first logical block.2. The apparatus of claim 1, further comprising a bad block mappingmodule configured to: access a bad block log during a start-up operationto make a controller for the solid-state storage operational from anon-operational state, wherein the bad block log comprises the bad blockinformation associated with the bad block; and create in memory a badblock map comprising a mapping between the location of the bad block inthe first logical block and a corresponding location of a replacementblock to store data instead of the bad block.
 3. The apparatus of claim1, wherein: the bad block identifier module is further configured toidentify additional physical blocks as additional bad blocks, whereinthe additional physical blocks are associated with a plurality oflogical blocks in the array of solid-state storage elements; and the logupdate module is further configured to store additional bad blockinformation associated with the additional bad blocks from the pluralityof logical blocks in the second logical block in the array ofsolid-state storage elements, wherein the additional bad blockinformation comprises locations of the additional bad blocks in theplurality of logical blocks.
 4. The apparatus of claim 1, furtherconfigured to: return the at least one page previously reserved forstoring bad block information to be used for storing data other than badblock information.
 5. The apparatus of claim 1, wherein the bad blockidentifier module is further configured to identify the at least onephysical block as the bad block in response to a determination that theat least one physical block is inappropriate for data storage, andwherein the bad block comprises a physical erase block.
 6. A system tomap bad blocks in solid-state storage, the system comprising: asolid-state storage array comprising two or more solid-state storageelements, wherein each solid-state storage element comprises a pluralityof solid-state storage cells; a solid-state storage controller coupledto the solid-state storage array to control the solid-state storagearray; and a bad block mapping apparatus coupled to the solid-statestorage array, wherein the bad block mapping apparatus comprises: a badblock identifier module configured to identify at least one physicalblock as a bad block, wherein the at least one physical block is one ofa plurality of physical blocks within a logical block in an array ofsolid-state storage elements; and a log update module configured tostore redundant bad block logs in at least two logical blocks in thearray of solid-state storage elements, wherein each bad block logcomprises bad block information associated with the bad block, whereinthe bad block information comprises a location of the bad block.
 7. Thesystem of claim 6, wherein the log update module is further configuredto store the redundant bad block logs in solid-state storage elementsthat are physically separate from one another.
 8. The system of claim 6,wherein the log update module is further configured to store eachredundant bad block log in a logical block spanning a plurality of thesolid-state storage elements.
 9. The system of claim 6, wherein the logupdate module is further configured to store, in each bad block log, anaddress of the corresponding redundant bad block log.
 10. The system ofclaim 6, wherein the bad block mapping apparatus further comprises a badblock mapping module configured to: access at least one of the bad blocklogs during a start-up operation to make a controller for thesolid-state storage operational from a non-operational state; and createin memory a bad block map comprising a mapping between the location ofthe bad block in the logical block and a corresponding location of areplacement block to store data instead of the bad block.
 11. A methodfor mapping bad blocks in solid-state storage, the method comprising:identifying first and second blocks as first and second bad blocks in anarray of solid-state storage elements; storing first bad blockinformation associated with the first bad block in a first page of alogical block corresponding to a bad block log for the array ofsolid-state storage elements; and storing second bad block informationassociated with the second bad block in a second page of the logicalblock corresponding to the bad block log for the array of thesolid-state storage device, the bad block log representing a time orderbetween the storing of the first bad block information and the secondbad block information.
 12. The method of claim 11, further comprisingconsolidating the first and second bad block information from the firstand second pages of the logic block into a single page of the logicblock.
 13. The method of claim 11, wherein the first page is a firstlogical page within the logical block, and the second page is a secondlogical page sequentially adjacent to the first logical page within thelogical block.
 14. The method of claim 11, wherein the first bad blockinformation is included in a version of the bad block log before anupdate, and the second bad block information is included in a delta fileto represent a difference between the bad block log before the updateand an updated version of the bad block log.
 15. The method of claim 11,wherein the second bad block information in the second page of the logicblock represents a record of change to a bad block log that is alreadyinclusive of the first bad block information in the first page of thelogic block.
 16. The method of claim 11, further comprising: storing afirst time indicator with the first bad block information, wherein thefirst time indicator comprises a time stamp associated withidentification of the first bad block; and storing a second timeindicator with the second back block information, wherein the secondtime indicator comprises a time stamp associated with identification ofthe second bad block.
 17. An apparatus comprising: means for storingdata in a solid-state storage device; means for identifying data blockswithin the solid-state storage device as bad blocks inappropriate fordata storage; means for storing a bad block log with bad blockinformation associated with each of the bad blocks; and means forseparately storing incremental bad block information associated withadditional bad blocks.
 18. The apparatus of claim 17, furthercomprising: means for consolidating the incremental bad blockinformation with the bad block log in a shared storage location; andmeans for triggering the consolidation of the incremental bad blockinformation with the bad block log.
 19. The apparatus of claim 18,further comprising means for recovering at least one page within alogical block in which the bad block log is stored in response to theconsolidation of the incremental bad block information with the badblock log.
 20. The apparatus of claim 17, further comprising means forstoring at least one error indication with each instance of bad blockinformation stored in the bad block log.